Radio-phono-telephonic system



L. P. DURAND RADIO-PHONO-TELEPHONIC SYSTEM Filed Jan. 8, 1935 March 23, 1937.

Patented Mar. 23, 1937 UNI-TED STATES ATENT OFFICE Application January 8, 1935, Serial No. 915 in France January 9, 1934 11 Claims.

This invention relates to an apparatus for receiving wireless transmissions, transmitting and receiving line telephony, and recording and reproducing sound, and its object is to obtain a simple arrangement which will perform the various functions without interference by extraneous, low frequency oscillation due to unwanted couplings between the various switch contacts and other causes.

With this object in view the invention consists in the combination with a rectifying and amplifying tube having control grid and cathode, of a telephone line, a loud speaker, a microphone, a pick-up, a radio receiver, and means for selectively forming circuits for said elements operative to lead the input to the grid of said tube in the case of high-frequency currents in radio reception and in pick-up operations without the microphone, and to the cathode of the tube in telephonic and microphonic operations.

The invention is illustrated in the accompanying drawing which represents a diagram of the electric connections in an apparatus constructed according to the invention.

In said drawing l represents the transformer of the intermediate or high frequency circuit of a radio receiver; 2 is a tube for rectifying the waves transmitted to the secondary of transformer l; 3 is a loud speaker; 4 is a microphone;

5 is a pick-up; and 6 is a telephonic line belonging to any existing telephone. The tube 2 is provided. with a cathode as well as with a control grid.

These elements and the various circuits by means of which the apparatus performs all the functions for which it is intended, are selectively brought into action by means of a switching device to which switch blades 8, 9, l0, ll, l2, and I3, belonging to different switches, are coupled in known manner, said switches and the control therefor being mounted on a panel 1.

Blade 8 co-operates with two stationary contacts l4 and i5. Blade 9 which is mechanically coupled to blade 8 as shown in dotted lines cooperates with contacts l6 and H. Blade l0 cooperates with contacts l8 and I9. Blade ll cooperates with contacts 29 and 2t. Blade l2 cooperates with contacts 22 and 23. Blade l3 cooperates with contacts 24 and 25.

Contact i5 is connected through a wire 26 with one of the ends of the secondary of a transformer 21 the primary of which is connected through a'wire 23 with the plate of a second amplifying tube 29.-

L The-blade 8 is'connected through a wire 39 with one of the ends of the winding 3| of a loud speaker 3. The other end of winding 3| is connected through a wire 32 with the free end of the secondary of transformer 27.

Contact I4 is disconnected. I

Contact i6 is connected through a wire 33 with one of the ends of the secondary of a microphonic transformer 35 the other end of which is connected to the earth at T.

Contact I! is connected, through a wire 35, to the wire 6 of the telephonic line.

Contact E8 is connected through a wire 36, 36' to the wire 28 that connects the plate of tube 29 with the primary of transformer 21. A condenser 48, acting as coupling condenser, is inserted in wire 26, 26. Contact l9 is disconnected.

Contact 29 is connected through a wire 37 with the cathode of tube 2, said wire 31 being itself connected through a wire 3'! to the blade 9 of switch 1.

A biasing resistance 50 is inserted in this wire 31.

Contact 2! is connected, through a wire 38, with pick-up 5 which, on the other hand, is connected to the earth at T. Wire 38 is further connected, through a wire 39, with blade I 0, a filtering cell 40 being, for a purpose described later, interposed therebetween.

Contact 23 is connected through a wire 4| with one of the ends of the primary of the microphonic transformer 34 the other end of which is con nected through a wire 42 with one of the terminals of microphone 4. The other terminal of this microphone is connected through a wire 43 with blade I2, with a battery G4 inserted therebetween.

Contact 22 is disconnected.

Finally, contact 25 is connected through a wire 45 with wire 33 and blade I 3 is connected through Wire 66 with the wire 6 of the telephonic line; the other wire 6 of this telephonic line is connected to the earth at T".

The apparatus above described may further include an indicator 4! of known type, for instance a luminous tube filled with neon gas, which will react to the current and show, by variations in the intensity of the flow, for instance on transmitting speech, whether or not the voice is sulficiently strong.

The operation of the apparatus above described takes place as follows: I

(a) Radio reception In this case, the following contacts are made: Blade l2 with contact 22, blade H with contact Cal 20; blade III with contact I9; blade 9 with contact I6 and blade 8 with contact I5.

The radiophonic waves transmitted to the secondary of transformer I are rectified by tube 2. This tube 2 is acted upon at the grid. The cathode is connected to earth at T.

On the other hand, the circuit of the loud speaker 3 is closed and the radiophonic waves operate this loud speaker.

(27) Recording of the radio reception pick-up to vibrate and thus to record the sounds on a disc, band, or film, etc.

(o) Reproduction of the sounds thus recorded For this operation, .the setting is again as at (a), but blade I I is connected to contact stud 2|.

The low frequency current issuing from pick-up 5 is fed, on the one hand, to the earth at T and, on the other hand, through wire 38, contact 2| and blade I I, to the grid of tube 2.

The sounds that have been recorded are thus reproduced and the apparatus works as an electric phonograph.

(d) Recording of local sounds The switching device I is operated in such manner that the following contacts are made:

Blade I2 with contact 23; blade I I with contact 20; blade II] with contact I8; blade 9 with contact I6; and blade 8 with contact I4.

The microphone 4, under the effect of the sound waves acting thereon, produces variations of current which: issuing from one terminal of battery 44, flow through wire 43, blade I2, contact 23, wire 4|, the primary of microphonic transformer 34, wire 42, microphone 4 and finally, the other terminal of the battery 44.

By induction there is produced a current in the secondary of transformer 34 and this current is fed, through wire 33, contact I6, blade 9, and wire 31 to the cathode of tube 2.

The microphonic currents are amplified by tubes 2 and 28 and when issuing from the plate of tube 29 through wire 36' and coupling condenser 48, they are divided into two portions, one of which passes through device 41 and therefrom to the earth at T, while the other one passes, through wire 36, contact l8, blade I 0, wire 39, filtering cell 40, and pick-up 5, to the earth at T.

The recording takes place substantially in the same manner as explained in (b).

It should be noted that, as blade 8 is applied against contact I4, loud speaker 3 is not inserted in the circuit. Consequently, any resonance effeet between microphone 4 and loud speaker 3 is avoided.

(e) Reproduction of any recorded sound This is obtained in exactly the same manner as stated under (0). I

(f) Telephonic conversations The apparatus above described may also be utilized as a telephone. For this purpose, switching device is operated in such manner as to bring blade I3 against contact 25, blade 9 against contact I'l, blade 8 against contact I5, blade II against contact 20, and blade I2 against contact For receiving telephonic communications, the low frequency current from the telephonic line flows, on the one hand, to the earth at T through wire 6 and condenser 49. On the other hand, this current fiows through wire 6, wire 35, contact II, blade 9 and wire 31, to the cathode of tube 2. After amplification, there is obtained an induced current in the secondary of transformer 21 and the contact 8-I5 being closed, loud speaker 3 reproduces the conversation.

For transmitting, the sound waves are caused to strike microphone 4. The currents induced, as above stated in (d), in the secondary of transformer 34 shall fiow, on the one hand to the earth, with which the wire 6' of the telephonic line is connected, and, on the other hand, through wires 33, 45, contact 25, blade I3, and wire 45, to the wire 6 of said telephonic line.

(9) Recording of the telephonic conversations The switches remain as in (f) except blade III which is changed over to contact I8.

The current from the telephonic line flows, on the one hand, to the earth at T through wire 5 and condenser 49, and on the other hand to the cathode of tube 2 through wire 5, wire 35, contact Il, blade 9 and wire 31. This current, flowing through the biasing resistance 50, produces variations of tension of the grid of tube 2, which variations are exactly equal to those of the modulated current from the telephonic line.

After the amplification performed by tubes 2 and 29, the current supplied by said tubes flows to the recording pick-up 5, as explained in (b).

Oviously, the connections just above stated may be established together with those stated under (1) in such manner that the apparatus records all the conversations when it is used as telephone.

(h) Reproduction of the recorded telephonic conversations This is obtained in the same manner as stated in (c).

It should be noted that although the elements such as the microphone, the transformer, the pick-up, the telephonic line, etc., are connected with the same switching device, there is no risk of low frequency oscillations, due to unwanted coupling between the various switch contacts, being set up since tube 2 is attached both at the grid and at the cathode. With this arrangement, the efficiency or the working of the apparatus is not impaired.

It will also be noted that it is possible to alter in the known manner, the electric characteristics of pick-up 5 by connecting filtering cell 40 to the circuit when sounds are recorded and by disconnecting it when the sounds are being reproduced.

Owing to the arrangement that has just been disclosed, it is possible to obtain a perfect working of the apparatus as a telephone in which the sounds are amplified and reproduced by the loud speaker. For this purpose, it suifices to connect microphone 4 directly to the telephonic line 6, 6, and to connect the loud speaker circuit. Any effect of acoustic reaction between the loud speaker 3 and the microphone 4 which would produce a continuous whistling sound (Larsen effect) is wholly eliminated due to the fact that the resistance of the telephonic line is much lower than that of the coupling elements of the amplifier, so that the microphonic currents flow practically wholly through the telephonic line and do not reach the loud speaker. This result is due to the fact that there is thus produced a kind of damping through the absorption, by the telephonic line, of these microphonic currents, this absorption being quite sufiicient for eliminating the oscillations due to the reaction of the loud speaker on the microphone.

What I claim is: 1. A radio-phono-telephonic system for use in connection with a telephonic line which comprises,

in combination, a loud speaker, a microphone, a

pick-up, a radio receiver, an amplifying tube, having a control grid and a cathode, and means for selectively forming circuits for said elements operative to lead the input to the grid of said tube in the case of high frequency currents in radio operations and in pick-up operations without the microphone, and to the cathode of the tube in telephonic operations.

2. A radio-phono-telephonic system for use in connection with a telephonic line, which comprises, in combination, a loud speaker, a microphone, a pick-up, a radio receiver, an amplifying tube having a control grid and a cathode, at least one electric circuit for each of these elements, two stationary contacts in each of these circuits, and a switch including a plurality of movable blades each adapted to cooperate with a pair of these stationary contacts, for connecting at will any of these circuits or the telephonic line with said tube, said circuits being operated to lead the input to the grid of said tube in the case of high frequency currents in radio operations, and in pick-up operations without the microphone, and to the cathode of the tube in telephonic operations.

3. A system according to claim 2 including two circuits adapted to cooperate with the pick-up, according as the latter is used for recording sounds or for reproducing them, so as to modify the working characteristics of said pick-up, according as it is connected with one or the other of these two last mentioned circuits.

4. A system according to claim 2 in which said switch is so devised as to permit of branching the telephonic line simultaneously with two circuits, for recording the telephonic conversations.

5. A system according to claim 2 further including a biasing resistance connected to the cathode of the amplifying tube so as to produce variations of the grid tension of said tube equal to the modulated currents from the telephonic line when telephonic conversations are recorded.

6. A system according to claim 2 including coupling means for the amplifier having a resistance higher than that of the telephonic line, so that the oscillations that might be produced by the reaction of the loud speaker on the microphone when the system works as a telephone are eliminated.

'7. A system according to claim 2 including two distinct circuits adapted to cooperate with the pick-up and a supplementary switch for coupling said pick-up with either of said circuits, one of said circuits being so made as to correspond to the Working of the pick-up according to its normal characteristics and the other one including means for artificially correcting the internal impedance resistance of said pick-up according to requirements.

8. A system according to claim 3 including two distinct circuits adapted to co-operate with the pick-up, and a supplementary switch for coupling said pick-up with either of said circuits, the pickup having an internal resistance high enough for the reproduction of sounds, and means in one of said circuits for artificially correcting the internal impedance resistance of the pick-up as required for the recording of sound.

9. A system according to claim 2 including two distinct circuits adapted to co-operate with the pick-up, and a supplementary switch for coupling said pick-up with either of said circuits, one of said circuits being so made as to correspond to the working of the pick-up according to its normal characteristics and the other one including means for artificially correcting the internal impedance resistance or" said pick-up according to requirements, and means including a filtering condenser and reactance coil for connecting the pick-up to the output circuit of the amplifier.

10. A system according to claim 2 including two separate circuits for the telephonic utilization of the apparatus, one of said circuits being that of the loud speaker, and. a combined telephonic receiver in the other of these two circuits.

11. A system according to claim 2 including two separate circuits for the telephonic utilization of the apparatus, one of said circuits being that of the loud speaker, a combined telephonic receiver in the other of these two circuits, and means for simultaneously controlling both of the two last-mentioned circuits.

LOUIS PAUL DURAND. 

